1. Field of the Invention
The present invention relates to a hydraulic control system of an automotive automatic transmission.
2. Description of the Related Art
In an automatic transmission, gear shifting is generally performed in such a way that a transmission control unit TCU controls a plurality of solenoid valves for guiding hydraulic pressure so as to apply and release the pressure to and from specific friction elements, resulting in obtaining a target gear ratio in the transmission.
That is, if a shift lever is manipulated to indicate a target speed range, a manual valve in a hydraulic system responsively converts its ports to a corresponding speed range arrangement such that hydraulic pressure from an oil pump is distributed to expected hydraulic lines. The distributed pressure is selectively supplied to various friction elements via various valves under control of the TCU.
Thus, the shift performance of the automatic transmission is determined in accordance with how timely corresponding friction elements respond to the shift lever manipulation.
FIG. 4 shows a hydraulic circuit to be modified by adapting a hydraulic pressure control system of the present invention.
As shown in FIG. 4, hydraulic pressure generated by an oil pump 200 is regulated at a predetermined level by passing a regulator valve 202 and is then partially supplied to each friction element through a shift control part 204, and is partially supplied to a damper clutch control valve 208 via a torque converter control valve 206. Subsequently, the hydraulic pressure supplied to the damper clutch control valve 208 is fed as a damper clutch operation pressure in a torque converter TC and is partially fed as a control pressure to the shift control part 204 by being reduced via a reducing valve 210, or to the damper clutch control valve 208 under a control of a damper clutch control solenoid valve DCCSV.
The shift control part 204 comprises various solenoid valves, shift valves, a manual valve, and friction elements.
A forward clutch FWD/C of the shift control part 204 operates at all forward speed ranges using the hydraulic pressure fed from the manual valve 212 via a forward clutch control valve 214 under control of a forward clutch solenoid valve FCCSV, and a 3-4 clutch 3-4/C and a low-reverse brake LR/B operates respectively at forward 3 and 4 speed ranges and at P, R, N, and L ranges using the hydraulic pressure fed from the manual valve 212 via a 3-4/low-reverse control valve 216 which is controlled by control pressure of a 3-4/low-reverse solenoid valve LRSV and a 3-4/low-reverse timing valve 218 which is controlled by a L range pressure from the manual valve 212.
However, this conventional hydraulic pressure control system has a drawback in that there exist two separate solenoid valves for the damper clutch and the forward clutch so as to cause the hydraulic system and a control algorithm therein to be complicated.
Furthermore, the usage of the L range pressure as the control pressure for the 3-4/low-reverse timing valve causes a shift shock since hydraulic pressure is supplied to the low-reverse brake in a state where the pressure applied to the 3-4 clutch is completely released, when shifting the range from high speed of the D range to the L range.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a hydraulic control system of an automotive automatic transmission capable of preventing shift shocks during N-D and D-L range shift as well as simplifying a structure of the system.
To achieve the above object, a hydraulic control system of the present invention comprises a first clutch acting as an input element at first, second, and third forward speed ranges, a second clutch acting as the input element at third and fourth forward speed ranges, a third clutch acting as the input element at an R range, a fourth clutch operating at P, R, N, and L range for performing an engine brake function by stopping a one-way clutch at the first, second, and third forward speed ranges, a first brake acting as a response element at the P, R, N, and L ranges, a second brake acting as a response element at second and fourth forward speed ranges, a first switch valve for distributing hydraulic pressure controlled by a first solenoid valve to a damper clutch in a torque converter and to clutch control valves for the first clutch, and a second switch valve for distributing hydraulic pressure controlled by a second solenoid valve to the second clutch and the first brake.